The present invention relates to a method of a post-processing receiving a sheet with an image formed thereon by a method of image formation using such as a copier or a printing machine, executing a post-process such as stapling, punching, or stamping on the sheet, and a method of sheet alignment placing the sheet at the post-process position in a predetermined posture.
In general, sheet aligning devices of this kind are widely known to place sheets with images formed thereon by an image forming apparatus, on a tray in a predetermined posture for alignment, to execute a post-process such as stapling, stamping, or punching on the sheets and accommodate the sheets in a downstream housing stacker. The processing tray thus requires a sheet aligning mechanism that places each sheet at a predetermined position for alignment so that the sheets can be subjected to the post-process.
Such a sheet aligning mechanism has been incorporated into a post-processing apparatus such as the one disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2003-128332 (FIGS. 2 and 4)). According to the publication, sheets processed by the image forming apparatus are stacked and set on the processing tray through a sheet discharging port. A stable device located on the tray then staples and discharges the sheets to a housing tray located downstream of the processing tray. The processing tray thus comprises a conveying roller that can rotate forward and backward to carry a sheet from the sheet discharging port downstream along the processing tray. Once a trailing edge of the sheet is guided onto the tray, a roller is reversely rotated to switch back the sheet.
The processing tray further has a trailing end regulating member against which trailing ends of sheets are controllably abutted to stack the sheets with their trailing ends appropriately positioned. Although not shown in the drawings of the publication, the processing tray has a sheet widthwise aligning plate that controllably places a sheet at an appropriate position in a direction orthogonal to a conveying direction for widthwise alignment; the sheet widthwise aligning plate places one side of the sheet at a reference position. A sheet from the sheet discharging port is stacked and set on other sheets on the processing tray, and at the same time, placed at a predetermined position for alignment.
Further, in order to prevent a sheet from being buckled or bent and curled by the regulating member, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2002-193535 (FIG. 17)) discloses a sheet aligning mechanism that reduces a sheet conveying speed to abut the sheet against a regulating device (end fence) to prevent the sheet from being buckled or bent.
Furthermore, to allow a large number of sheet bundles to be distributed and arranged in order, for example, Patent Document 3 (Japanese Patent Laid-Open No. 2000-034051 (FIGS. 6 and 8)) discloses a jog device in a sheet handling apparatus comprising a sheet accommodating device on which a plurality of discharged sheets is stacked and accommodated the form of sheet bundles and a stacker in which the sheet bundles discharged by the sheet accommodating device are sequentially housed. With the jog device, every time the sheet accommodating device discharges a sheet, the sheet is placed at an appropriate position for alignment. As a result, the sheet is accommodated at a reference position. The sheet bundles are distributed on the sheet discharging stacker at alternately displaced positions.
As described above, to sequentially stack the sheets on the tray such as the processing tray while placing each sheet at a predetermined position for alignment, the conventional techniques require the sheet transfer device and the widthwise aligning member to act simultaneously on the sheet; the sheet transfer device transfers the sheet on the tray toward the sheet end regulating member, and the widthwise aligning device places the sheet at the appropriate position in the direction orthogonal to the conveying direction for widthwise alignment. The sheet transfer device is composed of a rotating member such as a roller or a belt. The widthwise aligning device is composed of an aligning plate that engages with a side edge of the sheet to movably press the sheet.
Thus, the conventional techniques require the sheet transfer device and the aligning device to simultaneously act in a conveying direction and in a direction orthogonal to the conveying direction. This allows the sheet transfer device to be easily kept in pressure contact with a sheet. Thus, when the sheet is placed at the appropriate position in the width direction, a rotating force may disadvantageously act on the sheet as a result of the relationship between a sheet centroid position, varying with the sheet size, and a sheet widthwise aligning position set by the aligning device. As a result, the aligning operation may result in the sheets inclined on the tray (skew state).
For example, as shown in FIG. 12, sheet transfer device 50 causes a conveying force F1 to act in the conveying direction (in the figure, the direction opposite to a sheet discharging direction). At the same time, widthwise aligning device 51 causes a conveying force F2 to act in the orthogonal direction below a sheet centroid position G1. At this time, since the conveying force F2 of the widthwise aligning device 51 is weaker than the conveying force F1 of the sheet transfer device 50, when one end a1 of a sheet is placed at a position a2 for widthwise alignment, a rotating force acts to move the sheet centroid position G1 to a position G2 to move the other end b1 of the sheet to a position b2. As a result, the sheet is rotated as shown in the figure and thus placed in an incorrect position, resulting in an inappropriate post-process.
Further, it is assumed that the sheet transfer device 50 exerts a strong conveying force (for example, high-speed conveyance) on a sheet. Then, for a thick sheet, the sheet abutting against a sheet trailing end regulating member 52 rebounds and is thus placed in an incorrect position. For a thin sheet, the sheet abutting against the sheet trailing end regulating member 52 has its leading end bent and is thus skewed during an aligning operation. Such a misaligned sheet causes an inappropriate post-process, for example, a stapling process.
The present inventors solve the leading end bending problem and the rebounding problem by placing the leading end (or trailing end) of a sheet along a regulating member on the tray, feeding the sheet at a high speed when the sheet is placed at an appropriate position in the width direction using a center reference or a side reference and then reducing speed immediately before the trailing end of the sheet reaches the regulating member. After the sheet is abutted against the regulating member, widthwise aligning device moves the sheet in the orthogonal direction for widthwise alignment. In the present invention, it is therefore suggested that a conveying force, acting in a direction in which the leading end of the sheet abuts against the regulating member during the above widthwise aligning movement, is applied to the sheet, and the sheet is prevented from being skewed by being placed along the regulating member.
Therefore, a main object of the present invention is to provide a method of a sheet alignment that, when a sheet is placed at an appropriate position on a tray for alignment, prevents the sheet abutting against a regulating member from being rebounded or curled and skewed during widthwise alignment.
Another object of the present invention is to increase an operating speed of an image forming apparatus and a post-processing apparatus that can orderly stack sheets on the tray after processed by the image forming apparatus and then execute a post-process on the sheets.
Further objects and advantages of the invention will be apparent from the following description of the invention.